Uphold value constraints of dataloader batch function
npm install dataloader-valuesdataloader is an awesome package used for batching/caching and plays really well with GraphQL.
The only purpose of this package is to format the array of values returned from a batch function to uphold dataloader constraints:
>* The Array of values must be the same length as the Array of keys.
>* Each index in the Array of values must correspond to the same index in the Array of keys.
That means this package will be useful if it is difficult or impossible for you to accomplish any of the following with your batch function:
* Fill in missing values
* Sort values by key
* Group flattened values by key
Note that missing values are filled in with null for keys with single values and [] for keys with many values.
``shell`
yarn add dataloader-values
orshell`
npm install dataloader-values
Consider the example from dataloader. Your implementation might look like this:`js
import DataLoader from 'dataloader';
import { alignSingleValues } from 'dataloader-values';
import batchFetchLocations from './batchFetchLocations'; // Your batch function
const locationLoader = new DataLoader(async keys => {
const values = await batchFetchLocations(keys);
const alignedValues = alignSingleValues({
keys,
values,
getKey: ({ id }) => id,
});
return alignedValues;
});
`
You can also return values grouped into arrays by key (e.g., in a one-to-many relationship). For instance:
`js
import DataLoader from 'dataloader';
import { alignManyValues } from 'dataloader-values';
import batchFetchComments from './batchFetchComments'; // Your batch function
const commentsLoader = new DataLoader(async keys => {
// Returns flattened, ungrouped values
const values = await batchFetchComments(keys);
// Returns values grouped into arrays by key
const alignedValues = alignManyValues({
keys,
values,
getKey: ({ postId }) => postId,
});
return alignedValues;
});
`
See tests for a better breakdown of the data transformation.
`typescript`
export declare function alignSingleValues
export declare function alignManyValues
Both exported functions expect an object with the following arguments:
Field|Description
---|---
keys|Array of DataLoader keys({ id }) => id`)
values|Array of values returned from batch function
getKey|Callback function that returns the key from a single value (e.g.,